Typical cameras have a limited depth of field (DOF), which often causes blur and loss of image detail. Some image refocusing techniques may improve the plane of focus and DOF of an image during or after the image capture. One way to (e.g. post-factum) refocus is to instant capture the entire light field by a plenoptic camera (4D data capture). However, this technique can lead to a significant reduction in image resolution. Other refocusing techniques use ‘focal stack’ approaches (3D data capture). ‘Focal stack’ is a set of images of the same scene captured at different focus settings and used to facilitate refocusing in real-time or by a post-processing. For this purpose, a ‘sweep camera’ physically sweeps its focal plane across a scene (axially) during the direct capture, directly recording focal stacks (unlike the light-field camera), hence preserving sensor spatial resolution and saving the computation power/rendering time. Alternative sweeping methods can even contain a dynamic scene captured within a finite time period and, therefore, include the motion within the scene. In a simpler way, captured focal stack can be used to blend in-focus (sharp) patches from individual images following registration and appropriate scaling or, alternatively, for post-refocusing.
While capturing an instant light field may be beneficial in some situations, capture within the duration of time can result in a unique processing/refocusing experience, such as simultaneous perception of the dynamic objects within the scene by a user (e.g., combined with the dynamic focusing). Focal sweep can be implemented in multiple ways. Since scene motion and camera-shake can lead to motion blur in the captured images, it is important to capture the entire focal stack in a short time period, typically by either translating the scene along the optical axis during image exposure, or by sweeping the image sensor relatively to the subject. For a given pixel size, frame rate, and f-number of the lens, the overall capture time and total image count are highly related to focal length and scene distance range.